Bis(trifluoromethylsulfonyl)imide (NTf2)-Based Ionic Liquids for Facile Methane Electro-Oxidation on Pt

Abstract

Methane electro-oxidation was investigated and systematically characterized on three different electrodes (i.e. platinum, gold and carbon electrodes) with six different ionic liquids (ILs) by Cyclic Voltammetry (CV). At platinum electrode in bis(trifluoromethylsulfonyl)imide (NTf2) based ionic liquids (ILs), facile methane electro-oxidation is observed suggesting a unique catalytic Pt-NTf2 interface for electron transfer reaction of methane. Little methane electro-oxidation signal is observed in ILs with other anions. The final methane oxidation products in [C4mpy][NTf2] is confirmed to be CO2 and water by in-situ infrared spectroelectrochemistry. In contrast to many reported methane catalytic oxidation systems, there is no incomplete methane oxidation products observed. The electrochemical oxidation of methane at Pt and [C4mpy][NTf2] interface depends on the methane concentration linearly (from 1%∼10 vol.% methane concentration). The characteristic of peak potential shifts of the oxygen redox processes in the multiple cycle CV study is consistent with the electrode reaction of oxygen coupled with chemical reactions of CO2 and water which further confirms the products of methane electrode oxidation are CO2 and water. The cumulative results lead us to propose a mechanism suggesting a potential catalytic system of methane oxidation in NTf2 based ILs that strongly depends on the properties of the ILs and the electrode materials.